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    <title>侧边导航栏</title>
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    <p><a href="2.11日上机作业.html" target="content">页面一</a></p>
         <p><a href="2.12日上机练习.html" target="content">页面二</a></p>
         <p><a href="2.12日上机作业.html"target="content">页面三</a></p>
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